Saw blades for cutting wood, metal, and the like often have a plurality of teeth cut into the outer edge of the blade. In many cases, the saw blade teeth are tipped with a hard material, such as carbide, or cobalt alloys such as STELLITE to reduce wear and to maintain sharpness.
When a sawtooth is tipped with carbide or some other hard metallic material, the tip of the tooth is oversized and must be ground to desired dimensions and tangential and radial clearance angles for cutting the proper kerf. The tangential clearance angle is viewed from above the tooth and measures the inward taper of the tooth from the tooth face rearward. The radial clearance angle is viewed from the face of the tooth and measures the inward taper from the tooth top toward the blade.
The teeth of both circular saw blades and band saw blades may be tipped with hard material, and must be ground to the proper dimensions. Band saws comprise an endless blade loop that has saw teeth cut into one or both sides of the outer edge or edges of the blade. All band saws are "handed." That is, the teeth are cut into the outer edges of the band saw such that the saw cuts a work piece as the blade moves in one direction or the other relative to the work piece. A "right-handed" band saw has teeth cut into the outer edge of the blade such that the teeth cut when the blade moves in one direction; a "left-handed" band saw blade has teeth cut into the outer edge of the blade such that the teeth cut when the blade moves in the opposite direction.
As used herein, the designation of a band saw as being either "right-handed" or "left-handed" is arbitrary. For example, a right-handed band saw could be defined as a saw that cuts when the band saw loop rotates in the clockwise direction. Maintaining the same orientation, a left-handed blade would thus be defined as a saw that cuts when the band saw loop rotates in the counterclockwise direction. Band saws that have teeth formed on only one side of the blade are referred to as single cut blades.
Some band saws have teeth cut into both outer edges of the blade loop. These band saws are commonly called double cut blades, or double cuts. With double cuts the teeth on each outer edge of the band saw cut the work piece when the blade rotates in one direction. Thus, a double cut band saw will cut a work piece, wood for example, as the wood is moved past the blade from either direction. However, for purposes of reference for side grinding the teeth, on one side of a double cut band saw the teeth are right-handed; the teeth on the opposite side of the blade are necessarily left-handed.
In most cases, prior apparatus for grinding tipped band saw teeth to proper dimension and clearance angles grind the teeth with the band saw loop oriented horizontally. Thus, the band saw blade is oriented on the grinding machine with the width dimension of the band vertical and the saw teeth extending upwardly. For purposes of reference herein, horizontal orientation of a band saw refers to the orientation just described wherein the width dimension of the band is in the vertical direction and the saw teeth extend upwardly. In contrast, as used herein, vertical orientation of the band saw loop refers to a band saw in which the width dimension of the band is in the horizontal orientation and the saw teeth extend horizontally.
With horizontally oriented prior grinding machines, a pair of grinding wheels operates to successively grind each tooth on the band saw as the teeth are successively moved past the grinding heads. These machines typically require a large amount of floor space since the band saw blade loop is laid out horizontally. Moreover, the space requirements are essentially doubled if the sawmill is using both right and left-handed blades or a double cut saw blade because a left-handed blade must be positioned on the opposite side of the grinding head than a right-handed blade would be.
Another drawback of prior side grinding machines is the amount of equipment that must be used to support the band saw blade. While the grinding heads of such machines typically have equipment to support that portion of the band saw blade near the heads, the back side of the blade loop must be supported by additional post brackets.
Additionally, most horizontal side grinders require a separate, powered or mechanical back-feed device to feed the band to and past the grinding heads. Thus, because indexing the band past the grinding heads requires a fair amount of force when the band is horizontally oriented, a separate back-feed must often be purchased, and the back-feed must be somewhat timed to the indexing mechanism on the grinding heads.
Finally, although side grinders such as those discussed below are capable of grinding either right-handed or left-handed blades, on many occasions a sawmill will purchase two separate grinding machines, one dedicated to right-handed band saw blades, and the other dedicated to left-handed blades to save on the amount of time needed to convert the machine from right-handed operation to left-handed operation. Thus, prior art side grinding machines did not include redundant indexing systems capable of feeding a right-handed saw blade in a first direction, and a left-handed saw blade in a second direction with either blade mounted in the same position on the machine. The use of two separate machines not only adds cost, but requires even more floor space than would be required if a single side grinder is used to grind both right- and left-handed blades.
U.S. Pat. No. 4,819,515 to Pfaltzgraff, which is assigned to the assignee of the present application, is an example of a side grinding machine that operates on horizontally oriented blade loops. Pfaltzgraff teaches an apparatus for grinding saw teeth in a saw blade wherein the tip of each tooth is independently measured and ground before advancing successively each tooth on the saw blade for grinding.
The Pfaltzgraff apparatus, which is operated under the control of a programmable controller, is capable of grinding both left-handed and right-handed band saw blades. However, the saw blade is laid out in a horizontal loop with the teeth extending upwardly so that the saw teeth are indexed past the grinding heads, which move vertically downwardly to grind each tooth. Right-handed blades are oriented in a loop on one side of the grinding heads, and left-handed blades are oriented on the other side. If only one side grinding machine is used, this essentially creates a figure eight pattern, with the associated work space dedicated to the operation being about twice as great as would be required if the apparatus were dedicated solely to grinding blades of the same hand.
In addition, with the Pfaltzgraff machine, the band saw must be supported by numerous separate post brackets positioned on the back side of the blade loop. A back-feed apparatus is also necessary to keep the band saw indexing properly. This added equipment adds cost and requires additional floor space.
Finally, moving band saw blades into working positions on any kind of side grinding apparatus can be difficult. These difficulties are especially pronounced on grinders in which the band saw is oriented horizontally. With the Pfaltzgraff machine, manipulating the band saw blade into working position is difficult since the entire band must be lifted over the grinding heads. Band saws for cutting raw lumber are often very large and heavy; lifting such a blade onto and off of a grinding machine typically requires the efforts of at least two people. In addition, teeth on a band saw that have been tipped with a hard material can be quite sharp, even before grinding. As such, it is desirable to reduce the amount of manual handling of band saws.
U.S. Pat. No. 4,023,446 to Annas et al. teaches a vertically oriented band saw profile grinder. A profile grinder grinds the inner or forward face of a saw tooth, contrasted to a side grinder that grinds the tangential and radial clearance angles. In Annas et al., a pair of grinders are oriented to grind the teeth on two band saw blades that are suspended from overhead supports in vertical, downwardly directed loops. The band saw blades are looped over and hang down from opposite wheels, and the grinders are positioned below the wheels in position to grind the teeth as the blades are indexed vertically into the grinding position. The indexing system of Annas et al. is incapable of indexing both right- and left-handed saw blades past the same grinding head.
Another band saw side grinder that grinds horizontally oriented band saw blades is disclosed in U.S. Pat. No. 4,418,589 to Cowart, Sr. Like Pfaltzgraff, Cowart, Sr. teaches the use of a programmable controller for supervising the grinding of saw blade teeth, in which the travel of opposed grinding wheels is controlled by precision limit switches.
From the forgoing it will be recognized that all of the prior art apparatuses for side grinding the teeth of a band saw blade suffer from a variety of drawbacks which include the requirements of large floor space dedicated to side grinding, additional support and back-feed equipment, and difficulties associated with handling and positioning the band saw in a working position on the grinding apparatus. Additionally, none of the prior art side grinders are capable of side grinding the teeth of both right-hand and left-hand saw blades, and double cut blades, without changing the position of the blade relative to the grinding heads and thereby effectively at least doubling the space and back support requirements of these grinding apparatus. As such, these prior art apparatuses are poorly suited to simple, economical grinding operations.